Some turboprop gas turbine engines include a propeller brake which prevents rotation of propeller by preventing the rotation of the power turbine and power shaft. Such a brake can be used when the aircraft is on the ground, to run the engine and use the rotating high pressure shaft to provide pressurized air through the high pressure compressor section and/or drive a generator to perform some of the functions of an auxiliary power unit while the power shaft is prevented from rotating. However, running of the engine with the rotation of the power turbine shaft being blocked may be detrimental to the performance of the engine. Moreover, the amount of air and/or power generated may be insufficient, particularly in a hot weather environment.